1. Field of the Invention
The present invention relates to a resonator and a chip-type filter using it, in particularly, to a 1/4-wavelength resonator and a chip-type filter using it.
2. Description of the Prior Art
FIG. 36 shows a perspective view of one example of an existing resonator that forms the background to this invention. The resonator comprises a dielectric substrate 1, and a ground electrode 2 is formed over almost all of one surface of it. On the other surface of the dielectric substrate 1, a linear pattern electrode 3 is formed so as to be opposite to the ground electrode 2. One end of the pattern electrode 3 is connected to the ground electrode 2 through an edge of the dielectric substrate 1. A microstrip line is formed by the dielectric substrate 1, the ground electrode 2 and the pattern electrode 3.
In addition, using this type of resonator, a chip-type filter is formed as shown in FIG. 37. In the chip-type filter, a ground electrode 2 is formed over almost all of one surface of the dielectric substrate 1. On the other surface of the dielectric substrate 1, two pattern electrodes 3 are formed so as to be opposite to the ground electrode 2. One end of each pattern electrode 3 is connected to the ground electrode 2 through one edge of the dielectric substrate 1. These pattern electrodes 3 are formed so as to be parallel to each other, and are electromagnetically coupled. A take-out electrode 4 is formed from each pattern electrode 3 toward an edge of the dielectric substrate 1. The take-out electrode 4 is formed so as to be separated at a certain distance from one end of the pattern electrode 3 that is connected to the ground electrode 2. In the chip-type filter, the filter is formed by the electromagnetic coupling of two microstrip lines.
In this type of resonator and chip-type filter, one end of the pattern electrode is connected to the ground electrode, and the other end of the pattern electrode is open. These resonators and chip-type filters are formed by forming many electrodes on a large dielectric substrate, then cutting the dielectric substrate and finally connecting the pattern electrodes to the ground electrodes. However, since the pattern electrodes and the ground electrodes are formed on both surfaces of the dielectric substrate, displacement of the positions where the dielectric substrate is cut from the correct positions can cause fluctuation in the distances between the open ends of the pattern electrodes and the ground electrodes, causing the capacitance between the pattern electrodes and the ground electrodes to vary so that the characteristics of the resonators and the chip-type filters will fluctuate.
When the resonator is used, it is desirable for the impedance to be matched to the external circuit. However, in the microstrip line resonator shown in FIG. 36, since the characteristic impedance is determined by the dielectric constant and dimensions of the dielectric substrate and the dimensions of the electrodes, there are cases in which matching to the external circuit is impossible. For this reason, it becomes necessary to match the impedance to the external circuit by such means as connecting LC components for impedance matching and inserting a trimming step.